[PATCH] D86534: [GVN] Preserve MemorySSA if it is available.

[Florian Hahn via Phabricator via llvm-commits]

fhahn updated this revision to Diff 288705.
fhahn added a comment.
Herald added a subscriber: danielkiss.

Fix MemorySSA update for PRE loads. They are inserted just before the terminator, so we can just use createAccessInBB with BeforeTerminator position and the defining access of the original load.

In D86534#2243422 <https://reviews.llvm.org/D86534#2243422>, @asbirlea wrote:

> Not exactly the path I had in mind (working on newGVN was), but that's a longer avenue and I'm curious to see the compile-time impact of preserving MSSA :-)

Ideally NewGVN would be ready, but unfortunately there are still a few bigger issues. I intend to pick this back up after wrapping up a few other things.

Preserving MemorySSA is crucial to stay compile-time competitive with LTO, geomean ReleaseLTO -0.58%, ReleaseLTO (link only) -1.24%

http://llvm-compile-time-tracker.com/compare.php?from=d24856f1e0485c1a619528359e3cfd3dc8d15857&to=062412e79fcfedf2cf004433e42036b0333e3f83&stat=instructions


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D86534/new/

https://reviews.llvm.org/D86534

Files:
  llvm/include/llvm/Transforms/Scalar/GVN.h
  llvm/lib/Transforms/Scalar/GVN.cpp
  llvm/test/Transforms/GVN/preserve-memoryssa.ll

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